In existing GSM or UMTS telecommunications networks, hereinafter generally referred to as GSM networks, GSM or UMTS subscribers from a given geographical area are attached to the network by a Mobile Switching Centre, MSC, which serves that area. When a GSM or UMTS subscriber, hereinafter generally referred to as subscriber, initially attaches to an MSC using a GSM or UMTS Mobile Station, MS, such as but not limited to a mobile telephone, a Personal Digital Assistant, PDA, or a laptop, the MSC initiates a Location Update procedure. The Location Update procedure involves updating the HLR of the subscriber by a suitable update message comprising the current location, in the form of an MSC address, of the subscriber. This Location Update procedure is hereinafter referred to as “initial” or “standard” or “regular” Location Update procedure, being the Location Update procedure known in the art. The update message, from the MSC to the HLR, initiating the Location Update procedure, is called an “initial subscriber mobility registration update message”.
The HLR of a subscriber is a central database where information concerning the subscriber is stored, such as account numbers, features, preferences, permissions, etc. During the regular Location Update procedure the HLR is updated, by the MSC, with the address of the MSC to which the subscriber is attached. It is in turn the responsibility of the HLR to send GSM subscription data for that subscriber to the particular MSC. The information stored in the HLR is also used for various other services, such as detaching from the MSC, as will be appreciated by those skilled in the art.
If the subscriber “moves” to another MSC, e.g. by changing the geographical location and entering the area served by another MSC, the HLR is contacted and updated again by this other MSC. The HLR will now send subscription data to that other MSC and will instruct the previous MSC to remove the subscription data for that subscriber. This procedure, know in the art, is called an inter-MSC location area update. In this way, the HLR always comprises the MSC address where the subscriber is registered.
However, the subscriber may move from one location area to another location area within an MSC. Such change corresponds to a location area update within an MSC, called an intra-MSC location area update and does not result in a Location Update procedure to the HLR. Neither is detaching and attaching within an MSC notified to the HLR. Accordingly, in a GSM network the HLR has limited information about the specific geographical location of the subscriber, as well as the status (attached/detached) of the subscriber.
The aforementioned limited information results in limitations in functionality of the HLR in those cases where the location area of the subscriber and/or the status of the subscriber (attached/detached) plays a role. Examples of such cases include:
Terminating Call Handling:
The MSC address stored in the HLR is used for terminating call handling features. However, in some regions, such as the Caribbean, one MSC serves multiple countries (islands). Each country has one Base Station Controller, BSC, corresponding to one location area. Since in the HLR only the MSC address and not the location area is stored, the HLR cannot properly handle a terminating call, because the terminating call handling should correspond to a location area and not to the MSC.
IP Multimedia Subsystem Centralised Services, ICS:
If IP Multimedia System, IMS, services are offered to subscribers in the GSM network via IMS Centralised Services, ICS, the subscriber needs to be registered in the IMS network. This registration should be aligned with the status (attached/detached) of the subscriber. As this status is not always updated in the HLR, the HLR cannot handle the IMS registration/deregistration for the subscriber.